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Goncalves B.,Indiana University Bloomington | Perra N.,Indiana University Bloomington | Perra N.,Complex Systems Computational Laboratory | Vespignani A.,Indiana University Bloomington | Vespignani A.,Institute for Scientific Interchange
PLoS ONE | Year: 2011

Microblogging and mobile devices appear to augment human social capabilities, which raises the question whether they remove cognitive or biological constraints on human communication. In this paper we analyze a dataset of Twitter conversations collected across six months involving 1.7 million individuals and test the theoretical cognitive limit on the number of stable social relationships known as Dunbar's number. We find that the data are in agreement with Dunbar's result; users can entertain a maximum of 100-200 stable relationships. Thus, the 'economy of attention' is limited in the online world by cognitive and biological constraints as predicted by Dunbar's theory. We propose a simple model for users' behavior that includes finite priority queuing and time resources that reproduces the observed social behavior. © 2011 Gonçalves et al.

de Montis A.,University of Sassari | de Montis A.,Complex Systems Computational Laboratory | Caschili S.,University of Cagliari | Chessa A.,Complex Systems Computational Laboratory | Chessa A.,University of Cagliari
Journal of Geographical Systems | Year: 2011

The aim of this paper is to study the dynamics of the commuting system of two insular regions of Italy, Sardinia and Sicily, inspected as complex networks. The authors refer to a 20-year time period and take into account three census data sets about the work and study-driven inter-municipal origin-destination movements of residential inhabitants in 1981, 1991 and 2001. Since it is likely that the number of municipalities (in this case, the vertices of the system) does not display sharp variations, the authors direct the study to the variation of the properties emerging through both a topological and a weighted network representation of commuting in the time periods indicated. © 2010 Springer-Verlag.

de Montis A.,University of Sassari | Caschili S.,University College London | Chessa A.,Complex Systems Computational Laboratory | Chessa A.,University of Rome La Sapienza | Chessa A.,Institute for Advanced Studies Lucca
European Physical Journal: Special Topics | Year: 2013

A major issue for policy makers and planners is the definition of "ideal" regional partitions, i. e. the delimitation of sub-regional domains showing a sufficient level of homogeneity with respect to some specific territorial features. In this paper, we compare some intermediate body partitions of Sardinia, Italy, with patterns that emerge from the workers and students' commuting. We apply grouping methodologies based on the characterization of Sardinian commuting system as a complex weighted network. We adopt an algorithm based on the maximization of the weighted modularity of this network and detect productive basins composed by municipalities with degree of cohesiveness in terms of commuters' flows. The results of this study lead us to conclude that the recently instituded provinces in Sardinia have been designed -even unconsciously- as labour basins of municipalities with similar commuting behaviour. © 2013 EDP Sciences and Springer.

Cerina F.,Complex Systems Computational Laboratory | Cerina F.,University of Cagliari | Zhu Z.,IMT Institute for Advanced Studies Lucca | Chessa A.,Complex Systems Computational Laboratory | And 3 more authors.
PLoS ONE | Year: 2015

Production systems, traditionally analyzed as almost independent national systems, are increasingly connected on a global scale. Only recently becoming available, the World Input-Output Database (WIOD) is one of the first efforts to construct the global multi-regional input-output (GMRIO) tables. By viewing the world input-output system as an interdependent network where the nodes are the individual industries in different economies and the edges are the monetary goods flows between industries, we analyze respectively the global, regional, and local network properties of the so-called world input-output network (WION) and document its evolution over time. At global level, we find that the industries are highly but asymmetrically connected, which implies that micro shocks can lead to macro fluctuations. At regional level, we find that the world production is still operated nationally or at most regionally as the communities detected are either individual economies or geographically well defined regions. Finally, at local level, for each industry we compare the network-based measures with the traditional methods of backward linkages.We find that the network-based measures such as PageRank centrality and community coreness measure can give valuable insights into identifying the key industries. © 2015 Cerina et al.

Zhu Z.,IMT Institute for Advanced Studies Lucca | Puliga M.,IMT Institute for Advanced Studies Lucca | Puliga M.,Complex Systems Computational Laboratory | Cerina F.,Complex Systems Computational Laboratory | And 5 more authors.
PLoS ONE | Year: 2015

The fragmentation of production across countries has become an important feature of the globalization in recent decades and is often conceptualized by the term "global value chains" (GVCs). When empirically investigating the GVCs, previous studies are mainly interested in knowing how global the GVCs are rather than how the GVCs look like. From a complex networks perspective, we use the World Input-Output Database (WIOD) to study the evolution of the global production system. We find that the industry-level GVCs are indeed not chain-like but are better characterized by the tree topology. Hence, we compute the global value trees (GVTs) for all the industries available in the WIOD. Moreover, we compute an industry importance measure based on the GVTs and compare it with other network centrality measures. Finally, we discuss some future applications of the GVTs. © 2015 Zhu et al.

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